Part one of this series on installation angles for rear-facing CRs, which explored using the level-to-ground line to determine the appropriate angle, ran in the last issue of SRN. This article considers another issue related to rear-facing CR angle: things to consider when the top of the CR contacts the vehicle front seatback. Unlike the issue of understanding how to read the level-to-ground line, which depends solely on the CR manufacturer as the source of guidance, this situation requires considering the advice of both the CR and vehicle manufacturer.

Vehicle Manufacturers Now Have Something to Say Looking to the standardized CPS curriculum for guidance, this subject is covered in Chapter 9 by saying, “A rear-facing CR can be installed so that it rests against the back of the vehicle seat in front of it if this is not against the CR manufacturer’s instructions.” This advice would be more accurate if it also qualified that the vehicle manufacturer must also allow it, since the situation involves both the CR and the vehicle seat.

When a CR presses against the back of the front passenger seat, caregivers should check for the presence of an advanced air bag (AAB) system in the front seat of the vehicle. AAB technology began to be phased in with the 2003 model year and is in all newer cars, minivans, light trucks, and SUVs made since the 2006 model year. AABs can be identified in the owner’s manual and by the language on the front-visor warning label. While there are a variety of AAB systems, many detect the presence and size of a front passenger seat occupant to determine if the passenger air bag should deploy in a crash. (Note: this is not an issue that affects the driver’s seat.)

A number of different technologies are used for occupant detection, and AABs that use certain types of weight sensors are the ones of main concern with regard to CRs (and any other object) applying pressure to the front passenger seatback. Depending on the vehicle, the pressure could “fool” the sensor into misjudging the size or presence of the front seat occupant. This could cause the air bag to deploy when it should be suppressed, or not deploy when it should. See the January/February 2010 issue of SRN for a more in-depth article on this subject.

Because of this risk, it is always important to check the vehicle owner’s manual for advice when the CR touches the seatback. Manufacturer input stating whether or not the AABs used in its models could be negatively affected by pressure on the seatback is also included in the 2011 LATCH Manual* bullet points for each manufacturer (Appendix B).

A representative of one company, Honda, told SRN that “light contact” should not be a concern. Honda’s description of “light contact” is that which would allow a sheet of paper to be easily pulled out from between the contact point of the CR and the seatback. In other vehicles, the manufacturer would have to be contacted for this type of specific advice.

The CR Manufacturers’ Point of View In many rear-facing CR manuals, no mention is made of whether the CR may or may not make contact with the vehicle seatback. SRN informally polled a sample of four CR representatives on this question and found the general consensus to be that this omission implies consent, so long as the contact does not push the CR into a too-upright position or place excessive pressure on the CR.

There are notable CR manufacturer exceptions to this, however. The Century Smart Move, discontinued nearly a decade ago but very popular in its day, brought this issue to the fore. The unique Smart Move design allowed a baby to ride reclined at more than 45 degrees and moved to a more protective, upright position during the moment of a crash. The space was required so that this motion would be unobstructed.Evenflo infant CRs are the major exception today. For many years, the manuals for these have had statements the same or similar to this warning found in the manual for the Evenflo Embrace: “Ensure there is at least one and a half inches (38 mm) of space between any part of the carrier and the vehicle seat that is closest to the child’s head.”

In a letter sent to NHTSA in 2003 (available at www.regulations.gov by searching docket #NHTSA-1998-4064), Evenflo explained that the reason for this space requirement has to do with the fact that vehicle front seats are made to yield in a rear-end collision in order to manage the loads experienced by front seat occupants. As the vehicle seats yield, the amount of rearward movement is dependent on many vehicle and crash factors, and in some instances there is potential for interaction between the yielding front seat and the rear seat occupant directly behind it. Regarding the possibility that this could cause injury, the company says, “Evenflo is aware of two rear-impact motor vehicle collisions where yielding front seatbacks allegedly constrained the natural rearward motion of an infant-only restraint, allegedly causing severe injuries to the child occupant.”

These reported cases involve only infant CRs, and Evenflo indicated it had no knowledge of any real-life, negative front seat interaction with a convertible type CR. Through subsequent testing, the company determined that a rear-facing convertible CR, being generally larger, places the top of the back of the CR in a position that is high enough on the seatback that it would pivot out of harm’s way in the initial impact. However, it found that a rapidly yielding vehicle front seat could, in some instances, interfere with the rotational motion of an infant seat, which is usually positioned lower. Since it found that an inch and a half clearance provides adequate space for even these smaller infant CRs to rotate out of the area of contact with a potentially yielding front vehicle seatback in a rear-end collision, this clearance became a requirement for all Evenflo infant CRs.

Evenflo specifies that this space must be maintained when the CR has a vehicle seat directly ahead of it, as when the CR is installed in either outboard position, so this is typically not a concern in most center rear installations. In addition, SRN has confirmed with Evenflo that this space is not required when the CR is installed in a school bus, since bus seats manage forces differently than passenger vehicles and do not yield rearward in a crash.

In the U.S., current FMVSS 213 test equipment does not include a front seat ahead of the test seat to assess potential interaction, nor is rear-impact sled testing of CRs required, so no performance parameters exist for these situations. Evenflo’s position, therefore, comes from research that goes above and beyond FMVSS 213, one example of the many types of voluntary tests that Evenflo and other CR manufacturers regularly undertake.
The Swedish Approach An entirely different way to look at this issue is found in the approach to CPS taken in Sweden. One of the techniques used there is to intentionally rest the top of the reclined, rear-facing CR on a solid surface ahead of it—the front seatback when installed in the rear or, more commonly, the dashboard for CRs installed in the front seat (with no active air bag).

By firmly resting the CR against a solid part of the vehicle, the Swedish objective is to create a situation in which the CR will not be able to rotate forward too much in a frontal crash, will be more stable in a side impact, and will generally achieve the desired result of moving less in a crash. Therefore, when using this approach, touching the seatback ahead is a desired installation outcome.
Thoughts from Transport Canada A recent study from Transport Canada also suggests that resting a rear-facing CR against the front vehicle seatback may be beneficial for yet another reason—it may lessen the chance that the head will experience excessive force or strike a part of the vehicle interior in a frontal collision. The three-year study looked at 82 in-car crash tests of 131 rear-facing car seats (mostly infant seats with bases) in a variety of vehicle types (mostly passenger cars) and at various speeds (mostly 30 mph). It found the dummy had unacceptable peak head acceleration levels in a troubling 18 percent of cases, resulting from direct head-to-front seat, head-to-handle, CR-to-front seat, or CR-to-console impacts.

The researcher, Suzanne Tylko, noted that installations that rested the CR against the vehicle seatback seemed to greatly mitigate head accelerations since the CR already contacted the seat before the crash, which may serve to limit forward motion and child momentum during the crash.
(The study can be found at www-nrd.nhtsa.dot.gov/pdf/esv/esv22/22ESV-000406.pdf.)
What This Means to CPSTs
As CRs trend somewhat bigger while vehicles trend smaller, CPSTs more and more often find themselves in situations that involve the CR touching the front seatback. Anytime this is the case, both the vehicle and CR owner’s manuals should be consulted and followed. Specific instructions regarding the CR exerting pressure on the front passenger seat in vehicles with an AAB should be found in the vehicle owner’s manual. This information also appears in the manufacturers’ listings in the 2011 LATCH Manual*.

Specific advice should also be sought from the CR manufacturer; if nothing is mentioned, this typically means that the manufacturer does not mind if the CR rests against the front seatback, provided the overall installation is still correct.
In CR and vehicle safety, there are sometimes instances in which trade-offs must be made due to the unknowns of a particular crash scenario, and this subject clearly is a case in point. The concern of Evenflo regarding the crash dynamics of rear-impact collisions stand in contrast with the conclusions of the Transport Canada study that finds that resting the CR in gentle contact with the front seat could mitigate forward motion and possible head injury in a frontal collision. Though it is helpful for CPSTs to be aware of these concepts, it is the manufacturers that must make the call on how to use their particular products. CR and vehicle manufacturers are constantly testing the performance of their own products, both through regulated and voluntary methods, so it is crucial to follow the most up-to-date manufacturer’s directions for the particular equipment in use.

NHTSA currently lists updates to testing procedures as a “significant project” in its priority plan, and Volvo has petitioned NHTSA to make improvements to the test buck to more accurately reflect a vehicle interior. It is possible that the results of these efforts will one day clarify installation techniques that will further enhance safety for rear-facing children.